oi" 
4 
~ Marcu 17, 1923] 
Societies and Academies. 
Lonpon. 
_ Royal Society, March 8.—A. B. Wood, H. E. 
Browne, and C. Cochrane: Determination of velocity 
of explosion-waves in sea-water ; variation of velocity 
with temperature. An accurate determination of 
the velocity of explosion-waves in the sea gives : 
(a) V=4955'5 (+1) ft./sec., at 16:95 (+0-1)° C, 
and salinity 35 per cent. 
(b) V=4836 (+2) ft./sec., at 6-0 (to-1)° C. and 
salinity 35-I per cent. 
' (c) V=4847 (+1°5) ft./sec., at 7-0 (+0-1)° C. and 
salinity 35-2 per cent. 
In the new technique developed, it is unnecessary 
to know the exact position of charge relative to 
receivers. The results lead to a mean value of 
10-9 ft./sec. per ° C. as the temperature-coefficient 
of velocity in the range 6° C. to17° C. The following 
expression represents the velocity at any temperature 
?° C. within this range, and at any salinity S (parts 
per thousand) : 
V=4627 + 13-7t- 0-120 + 3-738. 
The salinity-coefficient is approximately 3 to 4 ft. /sec. 
per i per cent. increase of salinity, the theoretical 
value being 3-73 ft./sec. per 1 per cent. No change 
was detected for charges varying in weight from 
9 0z. to 300 lb. of explosive and no variation with 
depth. The coefficient of adiabatic compressibility 
of sea-water at 16-95° C. and 35 per cent. is 
Co= 42-744 (+0-02)x10°*. Combining this with 
Ekman’s value of Cg, the ratio of the specific heats 
of sea-water under these conditions of temperature 
and salinity is y=1-0094+0-0005, in good agreement 
with 1-0090, deduced from thermo-dynamic data.— 
P. M. S. Blackett: The study of forked alpha-ray 
tracks. Forked alpha-ray tracks obtained by the 
Wilson condensation method were studied. The 
lengths of the tracks of the recoil atoms yield 
information concerning the relative ionisation due 
to different kinds of ionising particles, and of the 
average charge carried by them. Measurements of 
the angles between different parts of the tracks gave 
the masses of the recoil atoms in three particularly 
favourable cases——A. Egerton: On the vapour 
pressure of lead.—I. The vapour pressure is measured 
by effusion of vapour at low pressure through a hole 
of measured area. Temperature is maintained 
constant by a selenium cell relay arrangement 
within 1/3° C. for many hours at about 800° C. 
Pressures were measured to 1o-° mm. The vapour 
ressure of ordinary lead between 1200-600° absolute 
is expressed by the equation log p=7-908-9932/T. 
The latent heat of vaporisation of lead (A,) is 
47,000+ 1000 cal. The chemical constant of lead is 
1-84+0-2, agreeing well with the theoretical value 
(1-853) obtained from the relation 3/2 log M-C,=C. 
The vapour pressures of lead and the uranium-lead 
isotope appear to differ by 2 per cent., but the result 
is rendered uncertain by an unexplained lowering 
of vapour pressure which lead undergoes on pro- 
longed heating in vacuo.—A. C. Egerton and W. B. 
Lee: (1) Some density determinations. The Archi- 
medes method of determining densities is rendered 
more accurate by utilising certain mobile and heavy 
aie liquids which avoid air bubbles and damping 
difficulties, and increase the weight of liquid displaced. 
Ethylene dibromide and carbon tetrachloride were 
employed with accuracy. A satisfactory sample of 
metal for density determination is prepared by filter- 
ing, casting, and heating in vacuo. he density of 
lead is 11-3437 at 20° C. The probable error of the 
nine determinations on three different samples is 
NO. 2785, voL. 111] 
NATURE 381 

I part in 100,000, The maximum departure from 
the mean value for any single determination is less 
‘ than 1 part in 12,000. A sample of uranium-lead 
would have an atomic weight of 206-26 from the 
density obtained. (2) Separation of isotopes of zinc. 
Two sets of distillations of pure zinc have been 
carried out in high vacuum, under conditions to 
obtain a slightly different concentration of the isotopes 
in the final residue of the final distillate. The samples 
are cast im vacuo and seeded with a particular kind 
of zinc. The first distillations gave a residue of 
slightly increased density, but the distillate possessed 
the same density as the original zinc. The second 
distillations gave a residue of increased density 
(about 1 part in 3700) and a distillate of decreased 
density (about 1 part in 3000). Determinations on 
seven samples of ordinary zine give the density of zinc 
(prepared in the described way) as 7-1400 (the 
probable error being less than 1 part in 100,000), 
Flaws, allotropes, different physical conditions, and 
impurities are improbable. The amount of the 
separation agrees with Dempster’s observations of 
isotopes of weights extending over six units (namely, 
64-70), but is not so great as might be found for 
equal parts of 64 and of atoms of weights 66, 68, 
and 7o.—E. Hatschek and P. C. L. Thorne: Metal 
sols in non-dissociating liquids. I.—Nickel in toluene 
and benzene. Very stable sols of nickel in a medium 
free from ions can be produced by decomposing 
nickel carbonyl dissolved in mixtures of toluene and 
benzene, containing a small amount of rubber, at 
100° C. In the electric field the particles of disperse 
phase move to, and deposit on, both electrodes. 
Electrophoresis in fields of different strengths, all 
other factors being equal, shows that the amounts 
deposited are proportional to the first, or a lower, 
power of the potential gradient. Therefore positively 
and negatively charged particles are originally 
present in the sol. The sol resembles typical pro- 
tected aqueous sols, inasmuch as it is coagulated 
by liquids which are not solvents for the protective 
colloid, i.e. rubber. The coagulum is only very 
imperfectly peptised again by rubber solvents, such 
as toluene or benzene.—H. Hirata: Constitution of 
the X-ray spectra belonging to the L series of the 
elements. 
Zoological Society, February 6.—Sir S. F. Harmer, 
vice-president, in the chair.— Oldfield Thomas: 
(1) A new rock-kangaroo, Petrogale godmani, sp. 0. 
It is like P. assimilis, but with a whitish tail, broader 
nasals, and larger secator. Its habitat is Black 
Mountain, near Cooktown, N. Queensland. (2) Skull 
of a pygmy fruit-bat from Sumatra. The generic 
name Ethalops is proposed.—C. A. Adair Dighton : 
Coat-colour in greyhounds.—E. G. Boulenger: The 
experiments of Dr. Kammerer and others upon 
amphibians and insects——E. Leonard Gill: The 
Permian fishes of the genus Acentrophorus.—Charles 
F. Sonntag: On the vagus and sympathetic nerves 
of the terrestrial carnivoran—E. P. Allis: The 
péstorbital articulation of the palato-quadrate with 
the neurocranium in the Ccelacanthide.—G, S. 
Giglioli: On the linguatulid arachnid, Raillietiella 
furcocerca (Diesing, 1835), Sambon, 1922.—Mrs. Rita 
Markbreiter: Some Microfilaria found in the blood 
of birds dying in the Zoological Gardens, 1920-1922. 
February 20.—Dr. A. Smith Woodward, vice- 
president, in the chair.—D. Seth-Smith: Sexual dis- 
play of the Magnificent Bird-of-Paradise (Diphyllodes 
magnifica hunsteini)—Einar Lénnberg : Remarks *on 
some palearctic bears.—E. W. Shann : The embryonic 
development of the porbeagle-shark, Lamna cornubica. 
—Robert Gurney: Some notes on Leander longirostris, 
M.-Edwards, and other British prawns. 
